This invention relates to a disconnect switch which is particularly useful in metal encapsulated switching installations and which has a fixed main tubular contact and a movable main tubular contact which is guided in a stationary outer housing. The movable tubular contact contains an auxiliary contact which is longitudinally movable relative to the movable tubular contact and which makes connection with the stationary contact at a fixed auxiliary contact.
One known disconnect switch of this type (Siemens Operating Instruction SW 8378-220 "Load Disconnect Switch 3CB, 10 kV," pages 102/1 to 102/3 ) is designed as a load disconnect switch (circuit breaker) and has a movable auxiliary contact which acts during disconnect in such a way that an arc is formed only between a so-called sliding contact and a burn-off ring on the contact ring. Because of this arc, gas is liberated from the insulating material of the stationary outer part which escapes from the quenching cup with a strong flow, deionizing the switch gap. In the aforesaid disconnect switch, no quenching device is provided between the stationary main contact and the movable contact tube; the metallic connection via the movable auxiliary contact and the fixed auxiliary contact must therefore be maintained during opening until the switching gap is interrupted after the arc is extinguished. Thereupon, the movable auxiliary contact is pulled out of the fixed auxiliary contact, so that the disconnect switch is visibly separated.
It is an object of the invention to provide a disconnect switch for use at higher voltages in which the large switching gaps necessary in such designs can be obtained without resort to particularly fast operating drives. Here, the term pre-breakdown time is understood to refer to the time during which an arc occurs between the fixed contact and the movable contact when switching on or off.